Process for hydrogenation of naphthenic acid derivatives



Patented Apr. 19,1938

PROCESS FOR HYDROGENATION OF NAPHTHENIC ACID DERIVATIVES Wilbur A. Lazicr, New Castle County, Del., as-

signor to E. I. du Pont de Ncmours & Company, Wilmington, Del., a corporation of Delaware No Drawing.

Application April 1'7, 1936,

Serial No. 75,022 1501mm. (0]. 260-153) This invention relates to catalytic processes for the production of organic compounds oi an alcoholic character. More particularly it relates to a process for the catalytic reduction by means of elementary hydrogen of naphthenic acid esters and anhydrides to yield the corresponding alco-' hols or esters of the corresponding alcohols. Specifically the invention relates to and has as its principal object the catalytic hydrogenation of esters and anhydrides of naphthenic acids derived from petroleiun products and to the naph thenyl alcohols thus prepared.

This application is a continuation-in-part of my copending applications Serial No. 445,224, filed April 1'7, 1930 and Serial No. 584,573, filed January 2, 1932.

For many years the only known method for the reduction of carboxylic acid esters and anhydrides of carboxylic acids, including these derivatives of naphthenic acids, to the corresponding alcohols has. been by purely chemical means. The most successful procedure is that outlined by Bouveault and Blanc in 1904. This process involves preparing an ester and the use of metallic sodium and absolute alcohol as the re ducing agent. By this means alone it has been possible to prepare alcoholic derivatives of naphthenic acid derivatives for purposes of characterization. Thismethod, however, is so costly as to render its use prohibitive for the manufacture on a commercial sc' e of naphthenyl alcohols which might otherwise be very useful in the arts.

This invention has as an object the production of naphthenyl alcohols by the catalytic hydrogenation of naphthenic acid derivatives. A further object is the effecting of this conversion by the use of compound catalysts consisting of a plurality of hydrogenating metals or metal oxides. Other objects of the invention willbecome more apparent from the following description.

Through the medium of processes iully described in the'copending specifications to which reference has already been made, it has now become possible to realize on a commercial scale a technically and economically successful catalyt ic hydrogenation of esters and anhydrides of naphthenic acids such as are obtained from certain petroleums whereby alcohols are formed which correspond in the number of carbon atoms to. the acid derivatives used. Other products such as the corresponding saturated hydrocarbons and estersof the newly formed alcohols may also be prepared in this way by minor variations in the procedure used.

It has now been found, in accordance with the present invention, that carboxylic derivatives of naphthenic acids in which the carboxyl group is attached either directly to a saturated or partially'saturated non-aromatic ring of carbon atoms or to an alkyl side chain of the said cyclic com pound are amenable to catalytic hydrogenation to the corresponding primary alcohols when subjected to treatment with an excess of hydrogen at high temperatures and pressures in the pres ence of a suitable hydrogenation catalyst.

According to a preferred embodiment of the invention a naphthenic acid ester or an anhydride of a naphthenic acid is heated either in an autoclave in the presence of a hydrogenation catalyst under high hydrogen pressure or the naphthenic acid derivative to be hydrogenated is permitted to flow over a heated catalyst in a continuous manner togetherwlth an excess supply of compressed hydrogen.

The following examples will illustrate in greater detail how the invention may be carried out in practice: Example I A barium-containing copper-chromite catalyst is prepared as follows: To a solution consisting of 52 g. of barium nitrate and 436 g. of copper nitrate trihydrat'e dissolved in 1600 cc. of water there is added with stirring a second solution consisting of 252 g. of ammonium bichromate and 300 cc. of 28% ammonium hydroxide dissolved in 1200 cc. of water. The precipitate comprising the mixed chromates is filtered, dried and ignited. After two extractions with dilute acetic acid followed by washing, drying and powdering, the resulting barium-copper-chromite catalyst is used for the hydrogenation of the esters of'naphthenic acids without further treatment.

The ethyl esters of naphthenic acid were prepared as follows: A fraction of naphthenic acids (acid No. 322) boiling at to C. per 20 mm., obtained by refining Russian petroleum, was esterified with absolute ethyl alcohol in the presence of concentrated sulfuric acid. The esterified product, after the usual treatment to remove sulfuric acid and unreacted naphthenlc acids, was fractionally distilled, the fraction boiling at 110 to 156 C. per 20 mm. representing a yield of 86% of the theory.

A high pressure autoclave was charged with 3577 g. of the ethyl esters of Russian naphthenic acids prepared as described above (having a saponiflcation number of 260) and 286 g. of the copper-barium-chromite catalyst prepared as described above. Compressed hydrogen was introduced into the autoclave until a pressure of about 3000 pounds per square inch was attained. The contents of the autoclave were heated for 9 hours with stirring at a temperature of 260 to 270 (3., the high hydrogen pressure being maintained meanwhile by introduction of a fresh supply of gas. Hydrogen absorption was rapid at first, as evidenced by the steady fall of pressure, and continued for about 8 hours. The reaction product was removed from the autoclave and the catalyst was separated by filtration.

In a typical experiment the saponification value of the crude hydrogenated productamounted to about 16 as compared with 260 before hydrogenation, which values correspond to a reduction of the carboxyl content amounting to about 94%. The residual ester was destroyed by adding '76 g.

of potassium hydroxide to the clear filtered solution and heatirg on a steam bath to saponify the unchanged ester. The ethyl alcohol was then removed by distillation and the naphthenyl alcohols' recovered by distillation under diminished pressure. The overallyield of refined naphthenyl alcohols was 2318 g. or of the theoretical value. The product had a boiling point 01' 101 to 141 C. at 19 mm. and a hydroxyl number. of 332, corresponding in average molecular weight to monohydric alcohols having 11 carbon atoms.

Example II A quantity of the Russian naphthenic acids described in Example I was converted to the anhydrides by heating with an excess of acetic anhydride and removing by distillation the acetic acid formed from the water split off during the formation of the naphthenic anhydrides. One hundred and fifty grams of the anhydrides were heated with agitation for six hours in contact with 12 g.of the copper-barium-chromite catalyst described in Example I, at a temperature of 260 C. and under a hydrogen pressure of 3000 pounds per square inch. This treatment resulted in a decrease in the saponification number from an initial value of 329 to 161, which represents a complete conversion of the anhydrides to the corresponding esters (naphthenyl naphthenates). By renewing the catalyst and hydrogenating again at a temperature of 300 C. it was possible to convert the naphthenic esters thus formed insubstantial yields to the corresponding naphthenyl alcohols.

The present invention is applicable to derivatives of naphthenic acids selected from a wide variety of sources. Furthermore, considerable variation in such'fundamental constants as molecular weight and boiling point are comprehended under this invention, since materials from the more .common source are complex mixtures of different individual compounds and thereforesubject to change in properties depending on the treatment used for their purification. In the selectionof suitable sources of petroleum naphthenic acids for the preparationof the esters and anhydrides, either crude or refined acids may be employed. Preferably naphthenic acids of domestic or Russian origin are selected and refined by preliminary fractional distillation. If desired,v

er freedom from poisons which exert a deleterious effect on the hydrogenation catalyst.

The acids are converted into such neutral derivatives as the corresponding anhydrides or esters which are then converted to the alcohols, preferably by means of a liquid phase batch hydrogenation method although the vapor phase method may also be used successfully. v

By the term naphthenic acid derivatives it is meant to include only compounds which are convertible to the corresponding acids upon hydrolysis. The invention is applicable to compounds of the general formula:

where R. is a cycloaliphatic residue and X is an alkyl, aryl, aralkyl, or acyl radical. As examples of such acid derivatives may be mentioned the naphthenic esters including the glycerides as well as the esters of monohydric alcohols, and the acid anhydrides formed by heating naphthenic acids alone or in the presence ofthe anhydrides of other'acids.

The processes of the present invention are characterized by the use of an excess of hydrogen at temperatures and pressures somewhat higher than those ordinarily employed for such liquid phase hydrogenations as are carried out for the purpose of hardening fats and fatty acids. The temperatures and pressures used in the above examples are illustrative only. Temperatures ranging from about 200 C. up to the decomposition temperatures of the reaction products may be used although temperatures of about 300 to 400 C. are preferable. Pressures ranging from ,about 10 atmospheres up to the-limit which the apparatus will withstand are suitable. The preferred pressure is within the range of about to 250 atmospheres and depends upon the acid derivative treated, upon the degree of hydrogenation desired, and the desired freedom of the prodnot from by-products.

The hydrogenation of naphthenic acid derivatlves to the corresponding naphthenyl alcohols and other products may be carried out either in batch or continuous processes. In carrying out the continuous method "it isonly necessary to modify the catalyst so as to form suitable grains, asby briquetting the powders described in the foregoing examples. In carrying out the hydrogenation processes of this invention in a continuous reaction system, the rate at which the compounds to be hydrogenated should be passed over the catalyst to give optimum results 'is a function of the activity of the catalyst, the temperature, and the molecular weight of the compound hydrogenated. Ordinarily the rate will vary from 2 to 8 liquid volumes per hour per unit volume of catalyst, although higher rates may be employed at the expense of slightly lower conversions. The ratio of hydrogen to the naphthenic acid compound or the naphthenic derivative may be varied over a wide range but it is preferable to use a substantial molecular excess of hydrogen. Where a flow process is used it is preferable to employ about 2 to 10 moles of hydrogen per mole of naphthenic compound undergoing treatment. As has been stated, the process may be operated to produce alcohols and/or esters and hydrocarbons if desired. ,A long period of contact of the reactants with the catalyst in combination with higher temperatures favors the completeness of reduction of the esters to .alcohols, andif carried far enough to hydrocarbons. On the other hand, a short time of contact and a temperature nearer the lower operative limit favors the formation of esters.

Whereas the critical factors and inventive steps in the hydrogenation of the naphthenic acid derivatives to naphthenyl alcohols are the use of hightemperatures and pressures, it is understood that suitable catalysts may be selected from a number of diiierent hydrogenating metals and oxides. Mild-acting alcohol-forming hydrogenation catalysts well known to be suitable for the synthesis of methanol from carbon monoxide and hydrogen are in general also suitable for the production of naphthenyl alcohols from naphthenic acid derivatives. On the other hand, there are certain very energetic catalysts such as metallic nickel and iron which are known to catalyze the formation of hydrocarbons from carbon monoxide and hydrogen. These ferrous metal catalysts, when employed in the hydrogenation of naphthenic acid derivatives to naphthenyl alcohols; carry the reaction too far with the formation of hydrocarbons. Therefore, if the hydrogenation is to be operated for the production of naphthenyl alcohols to the substantial exclusion of hydrocarbons, it is preferable to select as the catalyst a composition comprising a member of the group of non-ferrous hydrogenating metals, e. g., copper, tin, silver, zinc, their oxides and chromites, and oxides of manganese and mag nesium. Elemental nickel, cobalt, and iron, when suitably supported on kieselguhr, may be used to efl'ect the reduction of naphthenic acid derivatives to naphthenyl alcohol under special conditions, such as very high pressures and low temperatures. If the temperature employed is sufllciently high, however, the product contains besides alcohol a preponderance oi hydrocarbons, and this disadvantage in most cases will prove so serious as to preclude their use, unless the hydrocarbons themselves are desired end products.

Particularly good results have been obtained with chromite catalysts prepared according to the method described in U. S. Patent 1,746,783, wherein a double ammonium chromate of a hydrogenating metal is heated to form a chromite catalyst. -As indicated in the examples, success has attended the use of mixtures of the chromites of two or more metals. The catalyst compositions disclosed in my copendingapplication Serial No. 715,509, flled March 14, 1934, are eminently suited to the use oi'the present invention. I prefer to use a chromite composition containing substantial amounts of zinc or copper chromites.

By means or the above-described invention the usefulness of the synthesis of alcohols from acids has been greatly amplified. Acids are generally more plentitully round in nature than the corresponding alcohols. Naphthenic acids, for example, occur abundantly in petroleum while there is no such ready source of the corresponding naphthenyl alcohols.' By means of catalytic reduction it is possible to make the corresponding alcohols available for a wide number of applications in the arts. The naphthenyl alcohols obtained by the hydrogenation of naphthenic acid derivatives are colorless, limpid liquids of pleasant odor that boil in the range of to C. at 20 mm. They may be used as such or, for further applications, they may be converted into their simple derivatives in the same manner as applied to the preparation oi any other aliphatic-type high molecular weight alcohol.

It is apparent that many widely different embodiments or this invention may be made without departing irom the spirit and scope thereof and,

excess of 200 C. and under a pressure of at least 10 atmospheres.

2. The process in accordance with claim 1 characterized in that the reaction is carried out at a pressure between 100 and '250 atmospheres.

- 3. The process in accordance with claim 1 characterized in that the reaction is carried out at a temperature of about 300 to about 400 C.

4. The process in accordance with claim 1 characterized in that the catalyst is a copper-containing catalyst.

5. The process in accordance with claim 1 characterized in that the catalyst is a hydrogenating metal chromite. s

6. The processin accordance with claim 1 characterized in that the catalyst is a hydrogenating metal oxide associated with chromium oxide.

7. The process in accordance with claim 1 characterized in that the catalyst is a chromite catalyst containing substantial amounts of zinc chromite.

8. The process in accordance with claim 1 characterized in that the catalyst is a chromite catalyst containing substantial amounts of copper chromite.

9. A process for the production of alcohols from naphthenic acid derivatives, which comprises catalytically hydrogenating in the liquid phase a member selected from the group consisting of naphthenic acid esters and anhydrides of naphthenic acids, at a temperature of about 300 to about 400 C. and at a pressure in excess of 500 atmospheres.

10. A process for the production of alcohols irom naphthenic acid derivatives, which comprises reacting in the liquid phase a member selected from the group'consisting of naphthenic acid esters and anhydrides of naphthenic acids with hydrogen in the presence of a hydrogenating catalyst, at a temperature of about 300 to about 400 C. and at a pressure of about 100 to about 250 atmospheres.

11. The process in accordance with claim 10 characterized in that the catalyst is a coppercontaining catalyst.

12. The process in. accordance with claim 10 characterized in that the catalyst is a hydrogenating metal chromite. I

13. The process in accordance with claim 10 characterized in that the catalyst is a hydrogenating metal oxide associated with chromium oxide.

14. A process for the production of alcohols,

which comprises reacting a mixture of ethyl esters of naphthenic acids with hydrogen, in the pres- .ence of a copper-barium-chromite catalyst, at a temperature of about 260 to about 270 C. and at a pressure of about 3000 pounds per squ. re inch.

15. A process for the production of alcohols, 

